1. Technical Field
The present disclosure relates to a touch detection device which can detect an external proximity object, a display device with a touch detection function including the same, and an electronic apparatus.
2. Description of the Related Art
In recent years, display devices with a touch detection function that includes a touch detection device configured to detect proximity operation with an external proximity object such as a finger and a stylus pen are well known. The display devices with a touch detection function are called touch panels. Such display devices include, in addition to a type of the display devices in which a touch detection unit is mounted on a display device such as a liquid crystal display device, a type of the display devices in which a touch detection unit is integrated with a display device such as a liquid crystal display device.
Several detection methods are known for the touch detection devices, including optical detection method, resistance-type detection method, and capacitance-type detection method. Among these, the capacitance-type detection method allows fabrication of the touch detection devices with a relatively simple configuration and enables the device to be driven with low power consumption. Display device with a touch detection function including such a touch detection device allows the user to input desired information through a touch detection unit, in a similar manner as in the case of using general mechanical buttons, by displaying various kinds of button images on the display device and allowing the user to perform a proximity operation for the display device with an external proximity object. Unlike an input device, such as a keyboard device, a mouse device, and a keypad which are externally coupled to a display device, the touch detection device can be provided substantially integrally with the display device. Accordingly, the touch detection device is provided in various electronic apparatuses, such as mobile phones, television receivers, digital cameras, note-type personal computers, and the like.
The capacitance-type touch detection device includes a first wiring and a second wiring which are stacked. A voltage is applied to one (drive electrodes) of the wirings, and a detection signal is detected in the other wiring (touch detection electrodes) (see Japanese Patent Application Laid-open Publication No. 2012-43298 (JP-A-2012-43298)). In the capacitance-type touch detection device, when an external proximity object is in proximity to a detection region where detection is performed with the drive electrode and the touch detection electrode, the value of a signal detected in the touch detection electrode changes. Based on the change, the capacitance-type touch detection device detects proximity of the external proximity object. It is also described in JP-A-2012-43298 that the width of pad portions at the end of the drive electrodes are varied depending on positions.
The touch detection device has a plurality of drive electrodes arranged so as to be adjacent to each other in a specified direction (array direction). In other words, the touch detection device has a plurality of drive electrodes juxtaposed in the array direction. To detect a touch, the touch detection device switches the drive electrode to which a voltage is applied in a time division manner, and detects signals through touch detection electrodes at each detection timing. Consequently, when a touch is performed in a region where one drive electrode is arranged, the touch is detected as a change in signals of touch detection electrodes which overlap with the one drive electrode in the vicinity of the touch position.
In the touch detection device, a drive circuit which supplies a driving signal is coupled with each of the drive electrodes via wiring. Since each of the drive electrodes is arranged in parallel, a distance between each of the drive electrodes and the drive circuit is different. Accordingly, a wiring length between each of the drive electrodes and the drive circuit also varies.
Each of the drive electrodes has a wiring resistance value which varies depending on the length of the wiring coupled with the drive circuit. More specifically, the wiring resistance value is larger as the length of the wiring coupled with the drive circuit is longer. A drive electrode which is coupled with a longer wiring has a larger wiring resistance value. The larger wiring resistance value leads to a larger time constant, so that the time taken from reception of a driving signal to attainment of a predetermined level becomes longer.
In designing a system of the touch detection device, a touch detection period, i.e., the time taken for applying a driving signal to each electrode, may be set on the basis of the time taken for a driving signal, which is supplied to the drive electrode having a largest time constant, to attain a predetermined level. Accordingly, as a difference in time constant between the drive electrode having a large time constant and other drive electrodes becomes larger, reduction in touch detection period becomes difficult.
For the foregoing reasons, there is a need for a touch detection device capable of reducing touch detection time in each drive electrode, and a display device with a touch detection function and an electronic apparatus including the same.